Method for fabricating a semiconductor device

ABSTRACT

A method for fabricating a semiconductor device includes receiving a silicon substrate having an isolation feature disposed on the substrate and a well adjacent the isolation feature, wherein the well includes a first dopant. The method also includes etching a recess to remove a portion of the well and epitaxially growing a silicon layer (EPI layer) in the recess to form a channel, wherein the channel includes a second dopant. The method also includes forming a barrier layer between the well and the EPI layer, the barrier layer including at least one of either silicon carbon or silicon oxide. The barrier layer can be formed either before or after the channel. The method further includes forming a gate electrode disposed over the channel and forming a source and drain in the well.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. One development in the scaling down process is the use of fin field effect transistors (FinFETs). However, the FinFET transistor greatly increases process complexity and therefore the cost of fabricating the FinFET transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purpose only. In fact, the dimension of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flow chart of a method for fabricating a semiconductor device for benefiting from one or more embodiments.

FIGS. 2-8 are cross sectional views of forming a semiconductor device using a method according to one or more embodiments.

FIGS. 9A and 9B are an example of a barrier layer reducing a dopant migrating from a well through a channel into an interfacial layer of a gate electrode according to one or more embodiments.

FIG. 10 is an example of a barrier layer improving drain induced barrier lowering (DIBL) of a transistor according to one or more embodiments.

FIG. 11 is an example of a barrier layer improving an effective drain current (Ideff) vs. a source side off current in saturation region (Isoff) of a transistor according to one or more embodiments.

FIG. 12 is an example of a barrier layer improving speed, such as frequency (f), and a consumed active power (W) of a transistor according to one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Referring to FIG. 1, a flow chart of a method 100 for fabricating a semiconductor device is illustrated. FIGS. 2-8 are cross sectional views of forming a semiconductor device 200 using the method 100. In the present embodiments, a semiconductor device is also referred to as a semiconductor structure or a transistor. It is understood that additional steps can be provided before, during, and after the method 100, and some the steps described can be replaced, eliminated, or moved around for additional embodiments of the method 100. The method 100 is an example embodiment, and is not intended to limit the present invention beyond what is explicitly recited in the claims.

The method 100 begins at step 102 by receiving or providing a wafer substrate. In some embodiments, the wafer substrate is a silicon wafer. Alternatively or additionally, the substrate includes another elementary semiconductor, such as germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; or an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP. In other alternatives, the wafer substrate includes a semiconductor on insulator (SOI) structure. The wafer substrate includes one or more conductive and/or dielectric films. In the various embodiments, the dielectric film includes silicon oxide, high k dielectric material film, or a combination of silicon oxide and high k dielectric material, and the conductive thin film for the gate electrode film includes doped polysilicon, or a metal, such as aluminum (Al), copper (Cu), tungsten (W), nickel (Ni), titanium (Ti), gold (Au), platinum (Pt) or alloy of the metals thereof. In one embodiment, the wafer substrate includes a doped epitaxial (EPI) layer, for example, boron doped P-type (positive charger) Si EPI layer.

The method 100 proceeds to step 104 by forming an isolation feature embedded in the wafer substrate. The isolation feature is used to isolate a plurality of wells, such as a P-well or an N-well, to be formed on the wafer substrate; P standing for positive charge (e. g. a hole) and N for negative charge (e. g. en electron). In some embodiments, the isolation feature is a shallow trench isolation (STI) feature. In other embodiments, the isolation feature includes silicon oxide, silicon nitride, or silicon nitride-oxide in one or more layers. The isolation feature may also include other isolation material.

One way of forming an isolation feature uses a lithography process, such as depositing a resist film on the wafer substrate, exposing the resist film deposited on the wafer substrate according to a pattern and developing the exposed resist film to form a resist pattern on the wafer substrate. The resist pattern is transferred to the wafer substrate by etching, such as dry etching or wet etching, a trench in the wafer substrate. A deposition process, such as a chemical vapor deposition (CVD) or a physical vapor deposition (PVD) is then used to fill the trench with an isolation material, such as silicon oxide, silicon nitride, or silicon nitride-oxide in one or more layers. A chemical mechanical polishing (CMP) process is used to remove any excess isolation material and planarize a surface of the wafer substrate. FIG. 2 is a cross sectional diagram including an isolation feature 204 embedded into a wafer substrate 202.

The method 100 proceeds to step 106 by forming a well in the wafer substrate. The well is surrounded by the isolation features. In other words, the well is isolated by the isolation feature. In some embodiments, the well includes a P-well for a NMOS (metal on silicon) transistor or an N-well for a PMOS transistor. The P-well is formed by using a positive charged dopant and the N-well is formed by using a negative charged dopant. In the present embodiment, a dopant used for forming a well is referred to as a first dopant. A lithography process is optionally used to define a location and dimension of an implant, and protect other area from the implant. An ion implantation process, such as boron for the P-well or phosphorus for a N-well, implants the first dopant into the well. FIG. 3 is a cross sectional diagram including a well 206 is disposed between the isolation features 204 embedded in the wafer substrate 202.

The method 100 proceeds to step 108 by performing a recess etching process to remove a portion of the well isolated by the isolation feature. In the present embodiments, the etching process removes approximately 5 to 20 nm of the well, which has a height (well height) ranging from approximate 60 to 70 nm. FIG. 4 shows a removed portion of the well 206 disposed between the isolation features 204.

After step 108, the method 100 forms a barrier layer and a channel layer in the recess. There are different ways to form the channel layer and the barrier layer over the well. FIG. 1 shows two alternative options, labeled A and B.

Referring to option A of FIG. 1, after step 108, the method 100 proceeds to step 110A to form a barrier layer over the well. The barrier layer is about 3 to 10 nm thick. In one embodiment, an O₂ implant process implants oxygen into the well at the recess to create a silicon oxide barrier layer. For example, the O₂ implant process applies O₂ at a concentration ranging from approximate 100×10⁴ to 100×10⁵ parts per million (ppm) under an electric field voltage ranging from approximate 2K to 5K volts at a tilt angle of about zero degrees over surface of the well. In another embodiment, a carbon process implants carbon into the well at the recess to create a silicon carbide barrier layer. FIG. 5A shows a barrier layer 208 formed over the well 206.

Continuing with option A, the method 100 proceeds to step 112A by forming the channel layer over the barrier layer. In one embodiment, the channel layer is formed by epitaxially growing a silicon layer (EPI layer) in the recess. In some embodiments, the EPI layer increases mobility of a charge, such as a positive charge or a negative charge, and therefore improves performance of the device. FIG. 6 shows a channel layer 210 disposed on the barrier layer 208.

Referring now to option B of FIG. 1, after step 108, the method 100 proceeds to step 110B to form the barrier layer and the channel layer. In the present embodiment, and as discussed with reference to option A, the channel layer is a Si EPI layer and has a thickness from about 5 to 20 nm. FIG. 5B shows the channel layer 210 disposed over the well 206.

Continuing with option B, the method 100 proceeds to step 112B by forming the barrier layer between the channel layer and the well. In one embodiment, the barrier layer includes silicon oxide and has a thickness of about 3 to 10 nm. The barrier layer is formed using an implantation process through the channel layer, such as an O₂ implantation process. As with option A, in one embodiment, the O₂ implantation process includes applying O₂ at a concentration ranging from approximate 100×10⁴ to 100×10⁵ ppm under an electric field voltage ranging from approximate 2K to 5K volts at a tilt angle of about zero degrees over surface of the well. FIG. 6 shows the barrier layer 208 formed between the channel layer 210 and the well 206.

After either option A or B, the method 100 proceeds to step 114 by forming a gate electrode over the channel layer. The gate electrode includes an interfacial layer and a gate layer disposed over the interfacial layer. In various embodiments, the interfacial layer includes silicon oxide or a high-k dielectric material layer. Also in various embodiments, the gate layer includes polysilicon or metal layer. One way forming a gate electrode includes using a deposition process, such as CVD, PVD, or an electro-plating process to deposit a gate material. A lithography process and etching process patterns the gate. FIG. 7 shows a gate electrode 212 disposed over the channel layer 210.

The method 100 proceeds to step 116 by forming source and drain regions. Forming the source and drain includes forming a light doped drain (LDD) region and forming heavier doped regions using a spacer formed along the sidewalls of the gate electrode. The spacer includes silicon oxide or high-k dielectric material. The source includes a P-source or an N-source, and the drain includes a P-drain or an N-drain. In the present embodiments, a dopant used for forming a source/drain is refereed to as a second dopant. Step 116 includes using an implantation process. Forming the source and drain also includes using a deposition process.

FIG. 8 shows the semiconductor device 200 including a spacer 214 disposed along sidewalls of the gate electrode 212, and a source 216 and a drain 218 formed on opposite sides of the gate electrode. It is understood that FIG. 8 is provided as an example, and other configurations and inclusion or omission of various items in the device 200 is possible.

FIGS. 9A and 9B illustrate examples 300 of how the barrier layer reduces dopant (e.g. boron) migration from a well, through the channel layer (e.g. Si EPI layer), and into an interfacial layer of a gate electrode. FIG. 9A represents element boron concentration profiles at the interface of the interfacial layer of the gate electrode and the Si EPI layer with or without the EPI layer or the barrier layer by using a surface chemical analysis tool, such as a secondary ion mass spectrometer (SIMS). FIG. 9B is an enlarged illustration of FIG. 9A, at the interface of the interfacial layer of the gate electrode.

The examples 300 include a profile 302 (baseline profile), a profile 304, a profile 306, and a profile 308. The profile 302 represents boron concentration at an interface area of an interfacial layer of a gate electrode and a channel without an EPI layer between the interfacial layer of the gate electrode and the well. The profiles 304 and 306 represent boron concentration at an interface area of an interfacial layer of a gate electrode and an EPI layer (channel) without a barrier layer. The profile 304 is from an EPI layer with a thickness of approximately 16 nm and the profile 306 is from an EPI layer with a thickness of approximately 18 nm. The profile 308 represents boron concentration at the interface area of an interfacial layer of a gate electrode and a Si EPI layer with a barrier layer between it and the well, as taught in the previous discussion and figures. In the examples 300, the Si EPI layer reduces about 30% of the boron in an interfacial layer of a gate electrode as shown in the profiles 304 and 306, as compared with the profile 302. The Si EPI layer with a barrier layer, such as an O₂ implant layer, reduces about 58% of the boron in an interfacial layer of a gate electrode as shown in the profile 308 compared with the profile 302.

FIG. 10 is a sample 320 of a barrier layer improving a drain induced barrier lowering (DIBL) value of a transistor, such as an NMOS transistor. A trend line 322 is for an NMOS transistor without an EPI layer as a channel; a trend line 324 is for an NMOS transistor with an O₂ implant barrier layer formed before the Si EPI layer; and a trend line 326 is for an NMOS transistor with an O₂ implant barrier layer formed after the Si EPI layer. In the sample 320, the DIBL is improved from approximate 10 to 15 mV with the barrier formed before or after an EPI layer is grown by comparing the trend line 322 with the trend line 324 or the trend line 326.

FIG. 11 is a sample 340 showing how the barrier layer improves an effective drain current (Ideff) vs. a source side off current in saturation region (Isoff) of a transistor, such as a PMOS transistor. A trend line 342 is for a PMOS transistor without an EPI layer; a trend line 344 is for a PMOS transistor with an O₂ implant barrier layer formed before the Si EPI layer; and a trend line 346 is for a PMOS transistor with an O₂ implant barrier layer formed after the Si EPI layer. The trend line 344 shows that the Ideff-Isoff is improves by about 5% with an O₂ implant barrier formed before the Si EPI layer, as compared to the trend line 342, and the trend line 346 shows that Ideff-Isoff improves by about 8% with an O₂ implant barrier formed after the Si EPI layer, as compared to the trend line 342.

FIG. 12 is a sample 360 showing how the barrier layer improves consumed active power (W) and frequency (f) of a PMOS transistor. A trend line 362 is for a PMOS transistor without an EPI layer; a trend line 364 is for a PMOS transistor with an O₂ implant barrier layer formed before the Si EPI layer; and a trend line 366 is for a PMOS transistor with an O₂ implant barrier layer formed after the Si EPI layer. The trend line 364 shows that the power-frequency (W-f) is improved by about 0.5% with an O₂ implant barrier formed before the Si EPI layer, as compared to the trend line 362, and trend line 366 shows that the W-f is improved by about 1.5% with an O₂ implant barrier formed after the Si EPI layer, as compared to the trend line 362.

It is understood that various known processes can be used to fabricate the device 200, in addition to the unique processes and process sequences discusses above. Known processes include film deposition, lithography, etching, ion implantation process, chemical mechanical polishing, and cleaning. In some embodiments, the film deposition process includes a physical vapor deposition (PVD) process such as evaporation and DC magnetron sputtering, a plating process such as electrode-less plating or electroplating, a chemical vapor deposition (CVD) process such as atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), plasma enhanced CVD (PECVD), or high density plasma CVD (HDP CVD), ion beam deposition, spin-on coating, metal-organic decomposition (MOD), atomic layer deposition (ALD) process and/or other suitable methods.

In some embodiments, the lithography process includes coating a resist film on a wafer substrate, exposing the resist film by an optical lithography tool or an electron beam writer, and developing the exposed resist film to form a resist pattern for an ion implantation process or an etching process. Coating the resist film on the wafer substrate includes performing a dehydration process before applying the resist film on the wafer substrate, which can enhance an adhesion of the resist film to the wafer substrate. The dehydration process includes baking the substrate at a high temperature for a duration of time, or applying a chemical such as hexamethyldisilizane (HMDS) to the substrate. Coating the resist film on the wafer substrate includes a soft bake (SB). Exposing the resist film includes using a mask. Different kinds of masks include a binary mask (BIM), a super binary mask (SBIM), or a phase shift mask (PSM), which includes an alternative phase shift mask (alt. PSM) or an attenuated phase shift mask (att. PSM). Different kinds of optical lithography tools include an I-line, a deep ultraviolet (DUV), or an extreme ultraviolet (EUV) tool. Developing includes a post exposure bake (PEB), a post develop bake (PDB) process, or a combination thereof.

In some embodiments, the etching process includes a dry (plasma) etching, a wet etching, and/or other etching methods. For example, a dry etching process is implemented with an oxygen-containing gas, a fluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃), a bromine-containing gas (e.g., HBr and/or CHBR₃), an iodine-containing gas, other suitable gases and/or plasmas, and/or combinations thereof.

Thus, the present disclosure describes a semiconductor device and a method for making such device. In one embodiment, the semiconductor device includes a substrate having an isolation feature around a well in the substrate. The well includes a first dopant. The device also includes a source and a drain over the well, a gate electrode, and a channel between the source and the drain. The channel includes a second dopant. The device also includes a barrier layer disposed between the channel and the well. The barrier layer includes molecular oxygen.

In one embodiment, a method for fabricating a semiconductor device includes receiving a silicon substrate having an isolation feature disposed on the substrate and a well adjacent the isolation feature, wherein the well includes a first dopant. The method also includes etching a recess to remove a portion of the well and epitaxially growing a silicon layer (EPI layer) in the recess to form a channel, wherein the channel includes a second dopant. The method also includes forming a barrier layer between the well and the EPI layer, the barrier layer including at least one of either silicon carbon or silicon oxide. The barrier layer can be formed either before or after the channel. The method further includes forming a gate electrode disposed over the channel and forming a source and drain in the well.

In another embodiment, a method for fabricating a semiconductor device includes receiving a wafer substrate, forming an isolation feature in the wafer substrate, and forming a well having a first dopant in the wafer substrate. The method also includes etching a recess in the well and forming a layer in the recess, the layer having a second dopant. The method further includes forming an oxygen-containing barrier layer between the well and the layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor device, comprising: a substrate having a shallow trench isolation feature (STI) around a well in the substrate, wherein the well includes a first dopant and extends to a first depth within the substrate, wherein the STI extends to a second depth within the substrate that is greater than the first depth, and wherein the STI has a top surface opposite the substrate that extends along a plane; a source and a drain over the well, wherein at least one of the source and the drain includes a lightly doped drain feature; a channel between the source and the drain such that the channel does not extend above the plane, wherein the channel includes a second dopant; a gate electrode disposed over the channel; and a barrier layer disposed between the channel and the well, said barrier layer comprising silicon oxide, wherein the barrier layer extends under the lightly doped drain feature and has a top surface facing away from the substrate, wherein the lightly doped drain feature physically contacts a portion of the top surface of the barrier layer.
 2. The device of claim 1, wherein the gate electrode includes polysilicon.
 3. The device of claim 2, wherein the gate electrode includes an interfacial layer and a gate layer.
 4. The device of claim 3, further comprising a spacer disposed along sidewalls of the gate electrode.
 5. The device of claim 1, wherein the channel includes an epitaxial (EPI) silicon layer.
 6. The device of claim 1, wherein the barrier layer has a thickness between about 3 to 10 nm.
 7. The device of claim 6, wherein the channel has a thickness between about 5 to 20 nm.
 8. The device of claim 1, wherein a top surface of the source and a top surface of the drain extend along the plane.
 9. The device of claim 1, wherein the well extends into the substrate without extending under the STI.
 10. The device of claim 1, wherein the source and the well are bounded by the STI across an entire length of an outer edge of the source and an outer edge of the well.
 11. A semiconductor device, comprising: a silicon substrate having a shallow trench isolation feature (STI) and a well adjacent the STI, wherein the well includes a first dopant and extends to a first depth within the silicon substrate, wherein the STI has a top surface facing away from the silicon substrate, wherein the top surface of the STI extends along a plane, wherein the STI extends to a second depth within the silicon substrate that is greater than the first depth; a recess in the well; an epitaxially grown silicon layer (EPI layer) in the recess forming a channel, wherein the channel includes a second dopant; a barrier layer located between and physically contacting the well and the EPI layer, the barrier layer including silicon oxide, wherein the barrier layer extends under a lightly doped drain feature and has a top surface facing away from the substrate, wherein a portion of the top surface of the barrier layer is covered by the lightly doped drain feature physically contacting the top surface of the barrier layer; a gate electrode disposed over the channel; and a source and drain in the well, wherein one of the source and the drain includes the lightly doped drain feature, and wherein the channel and the barrier layer do not extend above the plane that the top surface of the STI extends along.
 12. The device of claim 11, wherein the barrier layer includes O₂.
 13. The device of claim 11, wherein forming the barrier layer includes controlling thickness of the barrier layer.
 14. The device of claim 13 wherein the gate electrode includes a metal.
 15. The device of claim 11, wherein the barrier layer has a thickness between about 3 to 10 nm.
 16. The device of claim 15, wherein the channel has a thickness between about 5 to 20 nm.
 17. The device of claim 16, wherein the well has a height (well height) between about 60 to 70 nm.
 18. The device of claim 11, wherein a top surface of the source and a top surface of the drain extend along the plane.
 19. The device of claim 1, wherein the STI has a top surface facing away from the substrate, wherein the top surface of the STI extends along a plane, and wherein the channel and the barrier layer do not extend above the plane that the top surface of the STI extends along.
 20. A semiconductor device, comprising: a substrate; a well formed in an upper portion of the substrate; an isolation feature contacting a sidewall of the well and extending below the well into the substrate; a barrier layer above the well and physically contacting a top surface of the well; a channel region above the barrier layer and physically contacting the barrier layer; a gate electrode above the channel region; and a source and a drain formed over the well, wherein a top surface of the channel region that extends from the source to the drain is substantially coplanar with a top surface of the isolation feature; wherein at least one of the source and the drain comprise a lightly doped drain feature; and wherein the lightly doped drain feature physically contacts a portion of the top surface of the barrier layer.
 21. The semiconductor device of claim 20, wherein a width of the barrier layer is greater than a width of the channel region. 